Method and apparatus for load-locked printing

ABSTRACT

The disclosure relates to a method and apparatus for preventing oxidation or contamination during a circuit printing operation. The circuit printing operation can be directed to OLED-type printing. In an exemplary embodiment, the printing process is conducted at a load-locked printer housing having one or more of chambers. Each chamber is partitioned from the other chambers by physical gates or fluidic curtains. A controller coordinates transportation of a substrate through the system and purges the system by timely opening appropriate gates. The controller may also control the printing operation by energizing the print-head at a time when the substrate is positioned substantially thereunder.

The application claims the filing-date priority of ProvisionalApplication No. 61/142,575, filed Jan. 5, 2009, the disclosure of whichis incorporated herein in its entirety; the application is acontinuation-in-part U.S. patent application Ser. No. 12/139,391 filedJun. 13, 2008, the disclosure of which is incorporated herein in itsentirety.

BACKGROUND

1. Field of the Invention

The disclosure relates to a method and apparatus for efficientdeposition of a patterned film on a substrate. More specifically, thedisclosure relates to a method and apparatus for supporting andtransporting a substrate on gas bearing during thermal jet printing ofmaterial on a substrate.

2. Description of Related Art

The manufacture of organic light emitting devices (OLEDs) requiresdepositing one or more organic films on a substrate and coupling the topand bottom of the film stack to electrodes. The film thickness is aprime consideration. The total layer stack thickness is about 100 nm andeach layer is optimally deposited uniformly with an accuracy of betterthan .+−0.1 nm. Film purity is also important. Conventional apparatusesform the film stack using one of two methods: (1) thermal evaporation oforganic material in a relative vacuum environment and subsequentcondensation of the organic vapor on the substrate; or, (2) dissolutionof organic material into a solvent, coating the substrate with theresulting solution, and subsequent removal of the solvent.

Another consideration in depositing the organic thin films of an OLED isplacing the films precisely at the desired location on the substrate.There are two conventional technologies for performing this task,depending on the method of film deposition. For thermal evaporation,shadow masking is used to form OLED films of a desired configuration.Shadow masking techniques require placing a well-defined mask over aregion of the substrate followed by depositing the film over the entiresubstrate area. Once deposition is complete, the shadow mask is removed.The regions exposed through the mask define the pattern of materialdeposited on the substrate. This process is inefficient as the entiresubstrate must be coated, even though only the regions exposed throughthe shadow mask require a film. Furthermore, the shadow mask becomesincreasingly coated with each use, and must eventually be discarded orcleaned. Finally, the use of shadow masks over large areas is madedifficult by the need to use very thin masks (to achieve small featuresizes) that make said masks structurally unstable. However, the vapordeposition technique yields OLED films with high uniformity and purityand excellent thickness control.

For solvent deposition, ink jet printing can be used to deposit patternsof OLED films. Ink jet printing requires dissolving organic materialinto a solvent that yields a printable ink. Furthermore, ink jetprinting is conventionally limited to the use of single layer OLED filmstacks, which typically have lower performance as compared to multilayerstacks. The single-layer limitation arises because printing typicallycauses destructive dissolution of any underlying organic layers.Finally, unless the substrate is first prepared to define the regionsinto which the ink is to be deposited, a step that increases the costand complexity of the process, ink jet printing is limited to circulardeposited areas with poor thickness uniformity as compared to vapordeposited films. The material quality is also lower due to structuralchanges in the material that occur during the drying process and due tomaterial impurities present in the ink. However, the ink jet printingtechnique is capable of providing patterns of OLED films over very largeareas with good material efficiency.

No conventional technique combines the large area patterningcapabilities of ink jet printing with the high uniformity, purity, andthickness control achieved with vapor deposition for organic thin films.Because ink jet processed single layer OLED devices continue to haveinadequate quality for widespread commercialization, and thermalevaporation remains impractical for scaling to large areas, it is amajor technological challenge for the OLED industry to develop atechnique that can offer both high film quality and cost-effective largearea scalability.

Manufacturing OLED displays may also require the patterned deposition ofthin films of metals, inorganic semiconductors, and/or inorganicinsulators. Conventionally, vapor deposition and/or sputtering have beenused to deposit these layers. Patterning is accomplished using priorsubstrate preparation (e.g., patterned coating with an insulator),shadow masking as described above, and when a fresh substrate orprotective layers are employed, conventional photolithography. Each ofthese approaches is inefficient as compared to the direct deposition ofthe desired pattern, either because it wastes material or requiresadditional processing steps. Thus, for these materials as well there isa need for a method and apparatus for depositing high-quality, costeffective, large area scalable films.

Certain applications of thermal jet printing require non-oxidizingenvironment to prevent oxidation of the deposited materials orassociated inks. In a conventional method, a sealed nitrogen tent isused to prevent oxidation. Conventional systems use a floating system tosupport and move the substrate. A floatation system can be defined as abearing system of alternative gas bearings and vacuum ports. The gasbearings provide the lubricity and non-contacting support for thesubstrate, while the vacuum supports the counter-force necessary tostrictly control the height at which the relatively light-weightsubstrate floats. Since high-purity nitrogen gas can be a costlycomponent of the printing system, it is important to minimize nitrogenloss to the ambient.

Accordingly, there is a need for load-locked printing system whichsupports a substrate on gas bearings while minimizing system leakage andnitrogen loss.

SUMMARY

The disclosure relates to a method and apparatus for preventingoxidation or contamination during a thermal jet printing operation. Thethermal jet printing operation may include OLED printing and theprinting material may include suitable ink composition. In an exemplaryembodiment, the printing process is conducted at a load-locked printerhousing having one or more chambers. Each chamber is partitioned fromthe other chambers by physical gates or fluidic curtains. A controllercoordinates transportation of a substrate through the system and purgesthe system by timely opening appropriate gates. The substrate may betransported using gas bearings which are formed using a plurality ofvacuum and gas input portals. The controller may also provide anon-oxidizing environment within the chamber using a gas similar to, ordifferent from, the gas used for the gas bearings. The controller mayalso control the printing operation by energizing the print-head at atime when the substrate is positioned substantially thereunder.

In one embodiment, the disclosure relates to a method for printing afilm of OLED material on a substrate by (i) receiving the substrate atan inlet chamber; (ii) flooding the inlet load-locked chamber with anoble gas and sealing the inlet chamber; (iii) directing at least aportion of the substrate to a print-head chamber and discharging aquantity of OLED material from a thermal jet discharge nozzle onto theportion of the substrate; (iv) directing the substrate to an outletchamber; (v) partitioning the print-head chamber from the outletchamber; and (vi) unloading the print-head from the outlet chamber. Inone embodiment of the invention, the print-head chamber pulsatinglydelivers a quantity of material from a thermal jet discharge nozzle tothe substrate.

In another embodiment, the disclosure relates to a method for depositinga material on a substrate. The method includes the steps of: (i)receiving the substrate at an inlet chamber; (ii) flooding the inletchamber with a chamber gas and sealing the inlet chamber; (iii)directing at least a portion of the substrate to a print-head chamberand discharging a quantity of material from a thermal jet dischargenozzle onto the portion of the substrate; (iv) directing the substrateto an outlet chamber; (v) partitioning the print-head chamber from theoutlet chamber; and (vi) unloading the print-head from the outletchamber. The print-head chamber pulsatingly delivers a quantity ofmaterial from a thermal jet discharge nozzle to the substrate.

In another embodiment, the disclosure relates to a load-locked printingapparatus, comprising an inlet chamber for receiving a substrate, theinlet chamber having a first partition and a second partition; aprint-head chamber in communication with the inlet chamber, theprint-head chamber having a discharge nozzle for pulsatingly metering aquantity of ink onto a substrate, the second partition separating theprint-head chamber from the inlet chamber; an outlet chamber incommunication with the print-head chamber through a third partition, theoutlet chamber receiving the substrate from print head chamber andexiting the substrate from a fourth chamber. In a preferred embodiment,the inlet chamber, the print-head chamber and the outlet chamber providean inert gas environment while the discharge nozzle pulsatingly metersthe quantity of ink onto the substrate. Although the implementation ofthe invention are not limited thereto, the inert gas environment can bea noble gas (e.g. argon, helium, nitrogen or hydrogen).

In still another embodiment, the disclosure relates to a load-lockedthermal jet printing system. The system includes a housing with an inletpartition and an outlet partition. The housing defines a print-headchamber for depositing a quantity of ink onto a substrate. The housingalso includes an inlet partition and an outlet partition for receivingand dispatching the substrate. A gas input provides a first gas to thehousing. A controller communicates with the print-head chamber, the gasinput and the inlet and outlet partitions. The controller comprises aprocessor circuit in communication with a memory circuit, the memorycircuit instructing the processor circuit to (i) receive the substrateat the inlet partition; (ii) purge the housing with the first gas; (iii)direct the substrate to a discharge nozzle at the print-head chamber;(iv) energize the thermal jet discharge nozzle to pulsatingly deliver aquantity of film material from the discharge nozzle onto the substrate;and (v) dispatch the substrate from the housing through the outletpartition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other embodiments of the disclosure will be discussed withreference to the following exemplary and non-limiting illustrations, inwhich like elements are numbered similarly, and where:

FIG. 1 is a schematic representation of a conventional substratefloatation system;

FIG. 2 is a schematic representation of an exemplary load-lockedprinting housing;

FIG. 3 is a schematic representation of the load-locked printing housingof FIG. 2 receiving a substrate;

FIG. 4 schematically shows the substrate received at the print-headchamber of the housing;

FIG. 5 schematically shows the completion of the printing process ofFIGS. 3 and 4;

FIG. 6 is a schematic representation of a print-head for use with theload-locked housing of FIG. 2; and

FIG. 7 is an exemplary load-locked system according to an embodiment ofthe invention;

FIG. 8 shows several types of substrate misalignment within the printsystem, and

FIG. 9 shows a substrate pattern including fiducials and initial locusof area viewed by a camera or other imaging devices.

DETAILED DESCRIPTION

FIG. 1 is a schematic representation of a conventional substratefloatation system. More specifically, FIG. 1 shows a portion of aflotation system in which substrate 100 is supported by air bearings.The air bearings are shown schematically as arrows entering and leavingbetween baffles 110. The substrate floatation system of FIG. 1 istypically housed in a sealed chamber (not shown). The chamber includesmultiple vacuum outlet ports and gas bearing inlet ports, which aretypically arranged on a flat surface. Substrate 100 is lifted and keptoff a hard surface by the pressure of a gas such as nitrogen. The flowout of the bearing volume is accomplished by means of multiple vacuumoutlet ports. The floating height is typically a function of the gaspressure and flow. In principle, any gas can be utilized for such asubstrate floatation system; however, in practice it is preferable toutilize a floatation gas that is inert to the materials that come intocontact with the gas. As a result, it is conventional to use noble gases(e.g., nitrogen, argon, and helium) as they usually demonstratesufficient inertness.

The floatation gas is an expensive component of the substrate floatationsystem. The cost is compounded when the printing system calls forsubstantially pure gas. Thus, it is desirable to minimize any gas lossto the environment.

FIG. 2 is a simplified representation of an exemplary load-lockedprinting housing according to one embodiment of the disclosure. Housing200 is divided into three chambers, including inlet chamber 210,print-head chamber 220 and outlet chamber 230. As will be discussed,each chamber is separated from the rest of housing 200 through a gate ora partition. In one embodiment of the disclosure the gates or partitionssubstantially seal the chambers from the ambient environment and fromthe rest of housing 200. In another embodiment of the disclosure (notshown), chamber 230 is not included in housing 200, and chamber 210 isutilized as both an inlet and an outlet chamber.

FIG. 3 is a schematic representation of the load-locked printing housingof FIG. 2 receiving a substrate. During operation, substrate 350 isreceived at inlet chamber 310 through inlet gates 312. Inlet gates 312can comprise a variety of options, including single or multiple movinggates. The gates can also be complemented with an air curtain (notshown) for minimizing influx of ambient gases into inlet chamber 310.Alternatively, the gates can be replaced with air curtains acting as apartition. Similar schemes can be deployed in all gates of the housing.Once substrate 350 is received at inlet chamber 310, inlet gates 312close. The substrate can then be detained at inlet chamber 310. At thistime, the inlet chamber can be optionally purged from any ambient gasesand refilled with the desired chamber gas, which is conventionallyselected to be the same as the floatation gas, e.g. pure nitrogen orother noble gases. During the purging process, print-head inlet gate 322as well as inlet gate 312 remain closed. Print-head inlet gate 322 candefine a physical or a gas curtain. Alternatively, print-head inlet gate322 can define a physical gate similar to inlet gate 312.

FIG. 4 schematically shows the substrate received at the print-headchamber of the housing. Air bearings can be used to transport substrate450 from inlet chamber 410 through print-head inlet gate 422 and intoprint-chamber 420. Print-head chamber 420 houses the thermal jetprint-head, and optionally, the ink reservoir. The printing processoccurs at print-head chamber 420. In one implementation of theinvention, once substrate 450 is received at print-head chamber 420,print-head gates 422 and 424 are closed during the printing process.Print-head chamber can be optionally purged with a chamber gas (e.g.,high purity nitrogen) for further purification of the printingenvironment. In another implementation, substrate 450 is printed whilegates 422 and 424 remain open. During the printing operation, substrate450 can be supported by air bearings. The substrate's location inrelation to housing 400 can be controlled using a combination of airpressure and vacuum, such as those shown in FIG. 1. In an alternativeembodiment, the substrate is transported through housing 400 using aconveyer belt.

Once the printing process is complete, the substrate is transported tothe outlet chamber as shown in FIG. 5. Here, print-head gates 522 and524 are closed to seal off outlet chamber 530 from the remainder ofhousing 500. Outlet gate 532 is opened to eject substrate 550 asindicated by the arrow. The process shown in FIGS. 3-5 can be repeatedto continuously print OLED materials on multiple substrates.Alternatively, gates 512, 522, 524 and 532 can be replaced with aircurtains to provide for continuous and uninterrupted printing process.In another embodiment of the disclosure, once the printing process iscomplete, the substrate is transported back to the inlet chamber 310through gate 322, where gate 322 can be subsequently sealed off and gate312 opened to eject the substrate. In this embodiment, inlet chamber 310functions also as the outlet chamber, functionally replacing outletchamber 530.

The print-head chamber houses the print-head. In a preferred embodiment,the print-head comprises an ink chamber in fluid communication withnozzle. The ink chamber receives ink, comprising particles of thematerial to be deposited on the substrate dissolved or suspended in acarrier liquid, in substantially liquid form from a reservoir. The inkhead chamber then meters a specified quantity of ink onto an upper faceof a thermal jet discharge nozzle having a plurality of conduits suchthat upon delivery to the upper face, the ink flows into the conduits.The thermal jet discharge nozzle is activated such that the carrierliquid is removed leaving behind in the conduits the particles insubstantially solid form. The thermal jet discharge nozzle is thenfurther pulsatingly activated to deliver the quantity of material insubstantially vapor form onto the substrate, where it condenses intosubstantially solid form.

FIG. 6 is a schematic representation of a thermal jet print-head for usewith the load-locked housing of FIG. 2. Print-head 600 includes inkchamber 615 which is surrounded by top structure 610 and energizingelement 620. Ink chamber 615 is in liquid communication with an inkreservoir (not shown). Energizing element 620 can comprise apiezoelectric element or a heater. Energizing element 620 is energizedintermittently to dispense a metered quantity of ink, optionally in theform of a liquid droplet, on the top surface of the thermal jetdischarge nozzle 640.

Bottom structure 630 supports nozzle 640 through brackets 660. Brackets660 can include and integrated heating element. The heating element iscapable of instantaneously heating thermal jet discharge nozzle 640 suchthat the ink carrier liquid evaporates from the conduits 650. Theheating element is further capable of instantaneously heating thethermal jet discharge nozzle 650 such that substantially solid particlesin the discharge nozzle are delivered from the conduits in substantiallyvapor form onto the substrate, where they condense into substantiallysolid form.

Print-head 600 operates entirely within the print-head chamber 220 andhousing 200 of FIG. 2. Thus, for properly selected chamber andfloatation gases (e.g. high purity nitrogen in most instances), the inkis not subject to oxidation during the deposition process. In addition,the load-locked housing can be configured to receive a transport gas,such as a noble gas, for carrying the material from the thermal jetdischarge nozzle 640 onto the substrate surface. The transport gas mayalso transport the material from the thermal jet discharge nozzle 640 tothe substrate by flowing through conduits 650. In a preferredembodiment, multiple print-heads 600 are arranged within a load-lockedprint system as an array. The array can be configured to depositmaterial on a substrate by activating the print-heads simultaneously orsequentially.

FIG. 7 is an exemplary load-locked system according to an embodiment ofthe invention. Load-locked system of FIG. 7 includes a housing withinlet chamber 710, print-head chamber 720 and outlet chamber 730. Inletchamber 710 communicates through gates 712 and 722. Print-head chamber720 receives substrate 750 from the inlet chamber and deposits organicLED material thereon as described in relation to FIG. 6. Gate 724communicates substrate 750 to outlet chamber 730 after the printingprocess is completed. The substrate exists outlet chamber 730 throughgate 732.

Vacuum and pressure can be used to transport substrate 750 through theload-locked system of FIG. 7. To control transporting the substrate,controller 770 communicates with nitrogen source 762 and vacuum 760through valves 772 and 774, respectively. Controller 770 comprises oneor more processor circuits (not shown) in communication with one or morememory circuit (not shown). The controller also communicates with theload-locked housing and ultimately with the print nozzle. In thismanner, controller 770 can coordinate opening and closing gates 712,722, 724 and 732. Controller 770 can also control ink dispensing byactivating the piezoelectric element and/or the heater (see FIG. 6). Thesubstrate can be transported through the load-locked print systemthrough air bearings or by a physical conveyer under the control of thecontroller.

In an exemplary operation, a memory circuit (not shown) of controller770 provides instructions to a processor circuit (not shown) to: (i)receive the substrate at the inlet partition; (ii) purge the housingwith the first gas; (iii) direct the substrate to a discharge nozzle atthe print-head chamber; (iv) energize the discharge nozzle topulsatingly deliver a quantity of material from the thermal jetdischarge nozzle onto the substrate; and (v) dispatch the substrate fromthe housing through the outlet partition. The first gas and the secondgas can be different or identical gases. The first and/or the second gascan be selected from the group comprising nitrogen, argon, and helium.

Controller 770 may also identify the location of the substrate throughthe load-locked print system and dispense ink from the print-head onlywhen the substrate is at a precise location relative to the print-head.

Another aspect of the invention relates to registering the substraterelative to the print-head. Printing registration is defined as thealignment and the size of one printing process with respect to theprevious printing processes performed on the same substrate. In order toachieve appropriate registration, the print-head and the substrate needto be aligned substantially identically in each printing step. In oneimplementation of the invention, the substrate is provided withhorizontal motion (i.e., motion in the x direction) and the print-headis provided with another horizontal motion (i.e., motion in theydirection). The x and y directions may be orthogonal to each other. Withthis arrangement, the movement of the print-head with respect to thesubstrate can be defined with a combination of these two horizontaldirections.

When the substrate is loaded onto a load-locked system, the areas to beprinted are usually not perfectly aligned in the x and y directions ofthe system. Thus, there is a need for detecting the misalignment,determining the required corrections to the motion of the print-headrelative to the substrate and applying the corrections.

According to one embodiment of the invention, the pattern or theprevious printing is detected using a pattern recognition system. Thispattern can be inherent in the previous printing or may have been addeddeliberately (i.e., fiducials) for the pattern recognition step. Bymeans of its recognition of the pattern, the misalignment of thesubstrate to the printing system's motion, direction or axis can bedetermined. This manifests itself as a magnification misalignment, atranslational misalignment and an angular misalignment.

FIG. 8 shows several types of substrate misalignment within the printsystem, including translational misalignment, rotational misalignment,magnification misalignment and combinational misalignment. For eachprint-head scan motion relative to the substrate, the patternrecognition system will look for and find/recognize the desired pattern.The pattern recognition system can optionally be integrated with thecontroller (see FIG. 7). The pattern recognition system will look forand find/recognize the desired pattern. The pattern recognition systemwill provide the degree of error/misalignment in the x and y directionsto the system's controller, which will then reposition the print-headand substrate to eliminate the error/misalignment. This means that forseveral motions of the print-head with respect to the substrate, themotion control system will check for misalignment and make the necessarycorrections.

Alternatively, an initial scan of the entire substrate can be performedby the pattern recognition system utilizing the x and y motionsavailable in the printing system. FIG. 9 shows a substrate patternincluding fiducials and initial locus of area viewed by a camera orother imaging devices. In FIG. 9, fiducials or alignment targets areidentified as boxes 910 in each replicated “pixel.” Each pixel in thisexample, and in many OLED applications, comprises three sub-pixels eachhaving a distinct color: red, green, and blue (RGB). The camera or thepattern recognition device initially focuses on an area of the substrateidentified by circle 930. Once the amount of misalignment is determined,the motion control system can compensate for the misalignment by causingthe x and the y directions to move in a rotated and translated set ofaxes x₁ and y₁ such that these axis are a linear combination of theprevious motions.

For either alignment technique, the printing control system will thencause the print-head to fire appropriately at the desired print axis asit scans the substrate. In the case of the embodiment described above,the print system will periodically use the pattern recognition system toupdate and adjust for any misalignment, causing the print-head to fireafter alignment has been achieved. Depending on the degree ofmisalignment, the required update and adjustment steps may have to berepeated more often during the printing operations. Alternatively, thepattern recognition system must scan the substrate initially to assessthe amount and direction of misalignment, then printing control systemwill utilize the misalignment information to adjust the print-headfiring accordingly.

While the principles of the disclosure have been illustrated in relationto the exemplary embodiments shown herein, the principles of thedisclosure are not limited thereto and include any modification,variation or permutation thereof. For example, while the exemplaryembodiments are discussed in relation to a thermal jet discharge nozzle,the disclosed principles can be implemented with different type ofnozzles. Moreover, the same or different gases can be used for floatingthe substrate and for providing a non-oxidizing environment within thechamber. These gases need not be noble gases. Finally, the substrate mayenter the system from any direction and the schematic of a tri-chambersystem is entirely exemplary.

1. A method for depositing an organic material on a substrate, themethod comprising the steps of: receiving the substrate at an inletchamber; flooding the inlet chamber with nitrogen, and sealing the inletchamber; floating the substrate using a gas bearing; directing at leasta portion of the substrate to a print-head chamber and, while floatingthe substrate using a combination of pressure and vacuum, discharging aquantity of the organic material from a discharge nozzle onto theportion of the substrate; directing the substrate to an outlet chamber;partitioning the print-head chamber from the outlet chamber; andunloading the substrate from the outlet chamber.
 2. The method of claim1, further comprising isolating each of the inlet chamber, print-headand outlet chambers from each other using at least one partition.
 3. Themethod of claim 1, wherein the inlet chamber and the outlet chamber arethe same.
 4. The method of claim 1, wherein said step of dischargingproduces a patterned film on the substrate.
 5. A method for depositingan organic material on a substrate, the method comprising the steps of:receiving the substrate at an inlet chamber; flooding the inlet chamberwith a chamber gas, consisting essentially of nitrogen, and sealing theinlet chamber; floating the substrate using a gas bearing; directing atleast a portion of the substrate to a print-head chamber and, whilefloating the substrate using a combination of pressure and vacuum,discharging a quantity of the organic material from a discharge nozzleonto the portion of the substrate, forming a patterned film thereon;directing the substrate to an outlet chamber; partitioning theprint-head chamber from the outlet chamber; and unloading the substratefrom the outlet chamber.
 6. The method of claim 5, further comprisingisolating each of the inlet chamber, print-head and outlet chambers fromeach other using at least one partition.
 7. The method of claim 5,wherein the inlet chamber and the outlet chamber are the same.
 8. Amethod for depositing an organic material on a substrate, the methodcomprising the steps of: receiving the substrate at an inlet chamber;flooding the inlet chamber with a chamber gas and sealing the inletchamber; directing at least a portion of the substrate to a print-headchamber and, while floating and controlling the substrate using thechamber gas and a combination of pressure and vacuum, discharging aquantity of the organic material from a discharge nozzle onto theportion of the substrate, forming a patterned film thereon; directingthe substrate to an outlet chamber; partitioning the print-head chamberfrom the outlet chamber; and unloading the substrate from the outletchamber.
 9. The method of claim 8, wherein the gas of the chamber gasand the gas bearing is nitrogen.
 10. The method of claim 8, wherein theinlet chamber and the outlet chamber are the same.
 11. The method ofclaim 8, further comprising isolating each of the inlet chamber,print-head and outlet chambers from each other using at least onepartition.